Actuator employing certain oxides that reversibly elaborate and take up oxygen



July 3, 1962 J. E. LINDBERG, JR 3,041, 2

ACTUATOR EMPLOYING CERTAIN OXIDES THAT REVERSIBLY ELABORATE AND TAKE UPOXYGEN Original Filed Sept. 8, 1958 JNVENTOR. JOHN E. L IND BE R6, JR. W4% (2) low temperatures and at low pressures.

United States Patent Ofifice 3,041,821 iatented July 3, 1962 9 Claims.(Cl. 60-23) This invention relates to improvements in method andapparatus for power transmission and actuation. It can be used toactuate any device capable of applying mechanical force, includinghydraulic systems, gas turbines, loudspeakers, valve actuators, and thelike. This application is a division of application Serial Number759,717, filed September 8, 1958, now abandoned.

Conventional power transmission or actuator systems are generally bulkyand excessively heavy. They consist of complex units whose overhaul andrepair are expensive. The operation of many of them depends upon liquidsor gases that must either be contained in rather large reservoirs toprovide potential energy, and/ or usually have to be circulated bypumps. In addition, many of these systems require close-fittingleakproof seals which are subject to failure at elevated temperatures.Often, various and sundry fittings, valves, and transmission lines arerequired as integral parts of the actuator unit.

Adequate power transmission systems are vital on modern aircraft, wherethey are used for retracting and lowering the landing gear, flapcontrol, afterburner control and many other things. But the actuatorsystems heretofore available have proved inadequate in the hightemperature environment experienced by high-speed aircraft and by guidedmissiles. Consequently, major aircraft companies have been trying todevelop 3000-p.s.i. actuator systems able to operate between -65 F. and1000' F. For example, current research is directed toward development ofhydraulic systems capable of operating in these environments, butperformance data on hydraulic pumps indicate that, as yet, no dependablepump has been developed which will function properly over the full -65F. to 1000 F. range. Even if there were such pumps, contemporaryhydraulic fluids are, at best, able to perform satisfactorily onlywithin the range of 100 F. to 700 F., while the seals that are necessaryin a hydraulic system have a relatively short life at 700 F.

Moreover, hydraulic systems have many disadvantages,

even if able to function properly. A pump external to the actuatingsystem is necessary, as are hydraulic accumulators in some cases; highpressure fittings, control valves, and transmission lines must beinstalled as an integral part of the system, and these result inexcessive bulk and weight. The fluids involved often constitute a firehazard, and the system must be primed before operation. In addition,when it is necessary to replace a defective unit because of a breakdown,other parts of the system are often alfected, resulting in expensiveprocedures.

One object of this invention is to provide an actuator (i.e.,power-transmission) system capable of satisfactory operation at 1)elevated temperatures in the range of 800 F. and higher and at highpressures, as well as at Another object is to provide an actuator thatdoes not depend upon liquids of any kind. It achieves these objects byutilizing certain thermodynamic properties of certain special oxides toalter the internal pressure of a container in which they are enclosed,in accordance with the temperature of the materials.

The actuating systems described herein are relatively simple, compact,and economical as compared to conventional systems, and in addition donot depend upon the use of external pumps or reservoirs. Thereby, thisinvention achieves the objects of providing a compact, relativelyinexpensive, simple, and economically operable actuator system.

A further aim of this invention is to provide actuating systems which donot employ valves, fittings, or fluid or vapor transmission lines, as donumerous present-day actuators, and which do not require primingoperations.

Over and above eliminating many disadvantages of conventional actuatingsystems, as well as solving the problem of elevated temperature andpressure actuation, this invention presents a much smaller fire hazardthan other contemporary systems, and will function with any source orsink of heat.

Other objects and advantages of the invention will appear from thefollowing detailed description of some preferred embodiments thereof.

In the drawings:

FIG. 1 is a view in side elevation and in section of an actuatorembodying the principles of this invention and incorporating asingle-unit cantilever bellows for control by temperature variation. Theactuator is shown in its contracted or hot position, and an accompanyingelectrical circuit is indicated diagrammatically.

FIG. 2 is a view like FIG. 1 but shows the bellows in its extended orcool position.

GENERAL PRINCIPLES OF THE INVENTION The principal phenomenon upon whichmy invention is based is the fact that certain oxides are capable ofingassing (taking in gas in either a chemical or physical action) uponthe application of heat and of degassing (also called out-gassing) uponthe removal of heat.

However, as will be seen, any of these ingassing or outgas-transferagent in a container of variable dimensions so constructed that thedimensions always conform to equilibrium conditions, i.e., to a balanceof the internal forces against the external forces. The application ofheat to such an enclosed gas-transfer agent then results in thealteration of the internal pressure within the container due to thetaking in of gas by the gas-transfer oxide, with the consequence thatthe container dimensions alter in order to maintain equilibrium. Thisdimensional alteration is accomplished by movement of some part of thecontainer, and this movement can be used to actuate or cause movement ofanother device which will perform useful work.

There are at least three mechanisms by which gases or vapors may betaken up by a solid. (1) The solid may chemically react with the gas orvapor. (2) The solid may physically adsorb the gas; then the gascondenses as a layer on the surface of the solid. (3) The solid mayphysically absorb the gas; then gas enters into the interior of thesolid in much the same manner as gas dissolving in a liquid. In manycases, the solid may taken up gas by both adsorption and absorption, andin many cases it is difiicult to determine the exact nature of themechanisms involved; so the generic term sorption and its derivativessorptive, sorbent, etc., are used to include both or either ofabsorption and adsorption. With the oxides used in this invention,sorption and desorption of a gas or vapor is reversible and can be madeto occur repetitively for an unlimited number of cycles.

For every sorptive condition of a mixture of the oxygen and the sorbantmetal, at any one temperature, there is a certain pressure at which thismixture will be in thermodynamic equilibrium. When the gas is athermodynamic phase of the sorbant substance, this pressure is oftencalled the equilibrium pressure; when the gas is not necessarily nativeto the sorbing substance, this pressure is often called the dissociationpressure; however, I shall use the terms interchangeably. It isgenerally true that under equilibrium conditions a change in any onethermodynamic variable causes a change in the others. Thus, theequilibrium pressure may be varied by changing the temperatu're. 7

When oxygen is sorbed or goes into solution in the metals used in thisinvention, heat is absorbed in the reaction in an endothermic reaction.The heat absorbed is termed the heat of solution.

It is diflicult to distinguish between a solution of oxygen and asolution of oxides. However, the formation of true solutions has beendetermined in silver, copper, and cobalt. Examples of the solubility ofoxygen in silver and copper are listed in Tables I and II.

Table I.--Slubility of Oxygen in Silver at 1 arm.

Pressure T C. Cm. /l00 g. 400 0.83 600 1.26 800 3.37

Table lI.S0lubility of Oxygen in Copper at 1 atm. Pressure T C. CmF/lOOg. 600 5.0 800 6.6 1050 11.0

GENERAL APPLICATION OF THE OXIDES OF THIS INVENTION TO THE PROBLEM OFACTU- ATION Y My invention provides means for altering the internalpressure of any closed container. If the container has dimensions whichare variable with internal pressure, then the resultant change of volumedue to change in internal pressure can be utilized to activate asuitable device. The container of variable dimensions used in thismanner thus becomes an actuator.

There are, as previously explained, many substances whose equilibriumgas or vapor content varies with temperature and pressure. In general,except for a few substances, the equilibrium pressure and temperaturehave a one-to-one correspondence. Hence, by inserting an oxygen-ingassedor degassed metal within a closed container, the internal pressure ofthe unit may be varied by the simpleexpedient of heating or cooling thegas-transfer agent.

An analytical expression has been developed for the purpose ofcalculating the change in volume of a container of variable dimensionsresulting from changing the temperature of a specified amount ofenclosed gas-transfer agent. The internal volume of the container isconveniently referred to as the loading chamber. The equation, which maybe referred to as the loading-chamber equation is:

where d is the density of unsaturated gas-transfer agent, in grams percc.

P is the initial pressure of the loading chamber, in atmospheres T isthe initial temperature of the loading chamber, in

Kelvin P is the final pressure of the loading chamber, in atmospheres Tis the final temperature of the loading chamber, in

Kelvin AS is the change in gas or vapor content of the gastransferagent, in cc., When pressure and temperature are varied from P T to P, T

V is the initial volume, in cc., of the loading chamber at pressure Pand temperature T V is the volume, in cc., of the gas-transfer agent inthe loading chamber V is the volume, in 00., of the loading chamber atpressure P and temperature T AV is V- V which is the change in volume ofthe loading chamber, in cc.

It is understood that initially the gas-transfer agent (i.e., the oxideof copper, silver, or cobalt) in the loading chamber is surrounded by,and is in equilibrium with, either an inert gas or vapor, or with a gasor vapor of the same chemical composition as that contained in, or to bereleased by, the gas-transfer agent. Helium, argon, zenon, and neon aretypical suitable inert gases.

Heat may be applied to the gas-transfer agent in many different ways. Adirect current filament may be used; an AC. current generator may beapplied to a filament embedded in the agent; the gas-transfer agent maybe heated by an inductive heating circuit consisting of a high frequencygenerator applied to an inductive heating coil which is either embeddedin or surrounds the gas-transfer agent; the gas-transfer agent may beheated by a flame that warms heat-conducting walls of a container; orthe gas-transfer agent may be heated by a solar concentrator having alens which serves to focus rays from the sun upon a reflector and thenceto the gas-transfer agent.

AN ACTUATOR WITH CANTILEVER-TYPE BELLOWS An actuator of variabledimensions, suitable for the employ of my invention and depicted in thedrawings, employs what is called a cantilever-type bellows 151. Thebellows 151 comprises several flat annular sheets 152 of suit-ablerefractory material or fabric which are joined alternately on theirouter periphery 153 and inner periphery 154, thus forming the flexiblebellows. The bellows 151 can be sealed at both ends by end members .155,1 56. The end member 156 may be stationary while at the other end themember is free to move and may contact the member to be actuated (notshown). When the pressure inside loading chamber 158 is lowered byheating a gas-transfer agent 160 of the unit, as by a filament 161,battery 162, leads 163, and potentiometer 164, the device moves to itsFIG. 1 position. When the internal pressure in the chamber 158 isincreased by cooling, the bellows 151 expands to an equilibrium positionshown in FIG. 2.

As an example, consider the use of the reaction between silver andoxygen, for which the solubility as a function of temperature is shownin Table I. The solution of oxygen in silver in the range of temperatureshown in the table is an endothermic reaction. Assume that in FIG. 2,100 grns. of silver oxide is used as the gas-transfer agent 160 and thatit is placed in the loading chamber 158 in equilibrium with oxygen at atemperature of 400 C. and a pressure of 1 atmosphere. The bellows 151 isin the expanded position as shown in FIG. 2.

If the oxide is now heated to 800 C., it may be seen by referring toTable I that 3.37-0.83=2.54 cm. of oxygen will be absorbed by thesilver, assuming that the external pressure against the actuator 150 isone atmosphere. Then if the eitective area of the actuator bellows 151is 2 cmfl, a contraction of As 2 1 7cm of the bellows will result. Thereaction between silver and oxygen is reversible so that if thetemperature of the oxide is lowered to 400 C. again, the actuator 150will expand to its initial position.

Cobalt and copper give similar reactions.

To those skilled in the art to which this invention relates, manychanges in construction and widely difiering embodiments andapplications of the invention will suggest themselves without departingfrom the spirit and scope of the invention. The disclosures and thedescription herein are purely illustrative and are not intended to be inany sense limiting I claim:

1. An actuator device, including in combination a container completelyenclosing a volume; means to expand the volume of said container tobalance the pressure in said volume with forces outside said container;a charge of material chosen from the group consisting of the oxides ofsilver, copper, and cobalt inside said container to give oil? gas whenthe temperature is lowered and to take in gas when the temperature israised, reversibly; an excess charge of oxygen in said container whenthe temperature is lowered, said charge of oxygen being taken in by saidmaterial when said temperature is raised; and means to heat and coolsaid material so as to increase and decrease the pressure inside saidcontainer, the resultant expansion and contraction of said containerbeing suitable for applying an actuating force to another device.

2. An actuator comprising a gas-tight bellows having a movable end; anoxide of metal chosen from the group consisting of cobalt, silver, andcopper in said bellows, which changes the internal pressure thereof byemitting quantities of oxygen large in proportion to said oxide when thetemperature of said oxide is lowered, and takes up oxygen when thetemperature of said oxide is raised; an excess supply of oxygen also insaid bellows; and means for heating said oxide.

3. An actuator device, including in combination: a sealed container; acharge of material chosen from the group consisting of the oxides ofcopper, silver, and cobalt inside said container; an excess charge ofoxygen in said container; means for changing the temperature of saidoxide at will to cause it to emit oxygen gas when cooled and take upoxygen gas when heated, as desired; and force-transmitting meansactuated by the emission and taking up of said gas within saidcontainer.

4. The device of claim 3, wherein said container also contains a chargeof inert gas.

5. The device of claim 3 wherein said means for changing the temperatureof said charge comprises an electric heating element inside saidcontainer and a source of electric power outside said container andelectrically connected to said element.

6. An actuator device, including in combination: a container completelyenclosing a volume; means to expand the volume of said container tobalance the pressure in said volume with forces outside said container;a gas-transfer agent inside said container and filling only a portionthereof, said gas-transfer agent comprising an oxide of metal chosenfrom the group consisting of cobalt, copper, and silver; an excesscharge of oxygen filling said volume and holding said volume expanded ata cool temperature, at least some of said excess oxygen being taken upby said gas-transfer agent when said gastransfer agent is heated,thereby reducing the pressure in said chamber; and means to vary thetemperature of said gas-transfer agent so as to change the pressureinside said container, the change in the volume of said container beingsuitable for applying an actuating force to another device.

7. The device of claim 6 wherein an inert gas is provided in saidcontainer in addition to said oxygen.

8. A power-conversion and transmission device, including in combination:a gas-tight container having at least one wall that is movable so as tovary the volume of said container in response to variations in internalpressure; an oxide of metal chosen from the group consisting of silver,cobalt, and copper inside said container; an excess charge of oxygeninside said container; and means for changing the temperature of said.oxide, so that it takes up oxygen when heated and emits oxygen whencooled, thereby varying the volume of said container.

9. An actuator comprising a gas-tight bellows having a movable end; anoxide chosen from the group consisting of copper, cobalt, and silver insaid bellows, said oxide emitting oxygen when cooled and taking inoxygen when heated; an excess supply of oxygen in said bellows; anelectrical heating filament in said oxide; a source of electrical power;and a circuit connecting said source to said filament.

References Cited in the file of this patent UNITED STATES PATENTS1,159,893 Browne et a1. Nov. 9, 191 5 1,756,688 Hutchinson Apr. 29, 19301,819,588 Bennett Aug. 18, 1931 2,271,307 Ray Jan. 27, 1942 2,627,911McCarty Feb. 10, 1953

1. AN ACTUATOR DEVICE, INCLUDING IN COMBINATION A CONTAINER COMPLETELYENCLOSING A VOLUME; MEANS TO EXPAND THE VOLUME OF SAID CONTAINER TOBALANCE THE PRESSURE IN SAID VOLUME WITH FORCES OUTSIDE SAID CONTAINER;A CHARGE OF MATERIAL CHOSEN FROM THE GROUP CONSISTING OF THE OXIDES OFSILVER, COPPER, AND COBALT INSIDE SAID CONTAINER TO GIVE OFF GAS WHENTHE TEMPERATURE IS LOWERED AND TO TAKE IN GAS WHEN THE TEMPERATURE ISRAISED, REVERSIBLY; AN EXCESS CHARGE OF OXYGEN IN SAID CONTAINER WHENTHE TEMPERATURE IS LOWERED, SAID CHARGE OF OXYGEN BEING TAKEN IN BY SAIDMATERIAL WHEN SAID TEMPERATURE IS RAISED; AND MEANS TO HEAT AND COOLSAID MATERIAL SO AS TO INCREASE AND DECREASE THE PRESSURE INSIDE SAIDCONTAINER, THE RESULTANT EXPANSION AND CONTRACTION OF SAID CONTAINERBEING SUITABLE FOR APPLYING AN ACTUATING FORCE TO ANOTHER DEVICE.